Ink jet head free of debonding between a substrate and ink flow path walls formed on said substrate

Abstract: An ink jet head having a plurality of ink flow path walls of forming a plurality of ink pathways by joining said plurality of ink flow path walls to a substrate for an ink jet head, said plurality of ink flow path walls being tightly bonded to said substrate without being debonded even in the case of continuously operating the ink jet head over a long period of time using highly alkaline ink. The ink jet head including a plurality of discharging outlets serving to discharge ink; a substrate for an ink jet head, said substrate including a plurality of energy generating elements capable of generating an energy for discharging ink from said plurality of discharging outlets and wirings electrically connected to said energy generating elements; and a plurality of ink pathways each having an ink flow path wall of forming one of the ink pathways by joining to said substrate, characterized in that each of the ink flow path walls is constituted by a specific epoxy resin composition (a) which is in the liquid state at room temperature, said epoxy resin composition (a) comprising (b) a hardening epoxy resin in the liquid state at room temperature as a main component and (c) an epoxy resin with a diepoxide structure having a siloxane bond incorporated into said epoxy resin (b).

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an ink jet head for discharging ink which is applied to an ink jet system. More particularly, the present invention relates to an improved ink jet head free of debonding between a substrate for an ink jet head and ink flow path walls formed on said substrate. The present invention includes an ink jet apparatus which is provided with said ink jet head. 2. Description of Related Background Art In recent years, progressively increasing attention has been paid to an ink jet system for conducting printing on a printing medium by discharging ink droplets towards said printing medium, since it can provide high speed, high density and high definition printing of a high quality at low noise and it is suitable for color printing and also for compact designing. An ink jet head which serves as a mechanism for discharging ink in such ink jet system is the most important factor for the ink jet system. The ink jet head has an extremely precise structure. Description will be made of such ink jet head with reference to FIG. 4. FIG. 4 is a schematically exploded view illustrating an example of the constitution of the ink jet head. In FIG. 4, reference numeral 101 indicates a silicon substrate for an ink jet head, having an electrothermal converting element as a discharging energy-generating element including heat generating resistors 103 and wirings 102 for said hear generating resistors formed on said silicon substrate by means of the thin-film forming technique. On the silicon substrate 101 having the electrothermal converting element thereon, there is disposed an ink flow path wall made of a photosensitive resin or the like of forming ink pathway walls 104a and a common ink chamber wall 104b. Reference numeral 105 indicates a top plate joined onto the ink flow path wall 104 such that it covers concaves formed by the ink flow path wall 104 to form ink pathways 108a and a common ink chamber 108b. Each ink pathway 108a contains the above-described heat generating resistor 103 positioned therein. Reference numeral 109 indicates an ink discharging outlet positioned at an end portion of the silicon substrate which is communicated with the ink pathway 108a. Reference numeral 107 indicates a common ink supply port disposed at the top plate 105. The common ink supply port 107 is covered by a filter 106 for ink which is fixed to the top plate 107. There are various proposals as for the process of producing an ink jet head of the constitution above described. U.S. Pat. No. 4,657,631 describes a typical process for producing such ink jet head. The process described in this patent document will be described with reference to FIG. 1. The process for producing an ink jet head according to the above patent document comprises the following six steps: step 1 (see, FIG. 1(a)) wherein a substrate 1 for an ink jet head which is provided with an energy generating element serving for discharging ink is provided, and a photosensitive resin layer 2 (comprising a positive type photoresist) is formed on the substrate 1; step 2 (see, FIG. 1(b)) wherein the photosensitive resin layer 2 formed in step 1 is subjected to light exposure through a patterning mask; step 3 (see, FIG. 1(c)) wherein the photosensitive resin layer 2 having subjected to light exposure in step 2 is patterned by way of subjecting said resin layer, whereby a plurality of relief solid layers 4 (that is, a plurality of relief patterns) are formed at respective positions on the substrate 1 where ink flow paths are to to be formed; step 4 (see, FIG. 1(d)) wherein a ink flow path wall-forming material 5 comprising a hardening resin is disposed to cover the relief solid layers 4 formed in step 3; step 5 (see, FIG. 1(e)) wherein the hardening resin is hardened; and step 6 (see, FIG. 1(f)) wherein the relief solid layers 4 are removed by way of dissolving them using an appropriate organic solvent such as halogen-containing hydrocarbon, ketone, ester, or alcohol or an aqueous alkali solution of potassium hydroxide or the like; whereby an ink jet head is completed. In the above-described process for producing an ink jet head, there is usually used a hardening resin as the ink flow path wall-forming material 5 as above described. However, a problem entails in this case in that a cure shrinkage is liable to occur upon hardening the hardening resin wherein a shrinkage stress is unavoidably effected. And such hardening resin is somewhat swelled when contacted with ink. This swelling of the hardening resin provides a stress in accordance with a change in the environmental temperature, particularly upon operating the ink jet head. In the case of an ink jet head having ink flow path walls comprised of the hardening resin, a debonding is liable to occur between the ink flow path walls and the substrate when the ink jet head is repeatedly used, because of the above described stress. This debonding entails a loss in the discharging energy to the ink pathways, wherein in the worst case, the discharging energy becomes insufficient such that no ink is discharged from a discharging outlet. Therefore, in the production of an ink jet head, an appropriate ink flow path wall-forming material is selectively used in order to prevent the ink flow path walls from being debonded from the substrate. In order that the ink flow path walls are prevented from being debonded from the substrate, there are known a manner wherein the ink flow path walls are formed with the use of an ink path wall-forming material having a reduced elasticity modulus so that they can absorb the foregoing stress provided in accordance with a change in the environmental temperature and another manner wherein the ink flow path walls are formed with the use of an ink path wall-forming material which is slightly swelled with ink so that they slightly provide such stress due to a change in the environmental temperature. However, any of these two manners is not sufficiently effective in practice. That is, such ink flow path wall-forming material having a reduced elasticity modulus is relatively large in terms of the swelling magnitude to ink and because of this, the ink flow path walls in accordance with any of the two manners are insufficient in terms of the stress absorbing efficiency. Thus, it is necessary for the ink flow path walls to be formed of a specific hardening resin having a relevant elasticity modulus while satisfying conditions relating to the swelling property to ink and the stress absorbing efficiency. Now, the swelling property of the ink flow path wall-forming material to ink can be represented by a term of "ink resistance". As for an ink flow path wall-forming material having a high swelling property to ink, it can be considered to be low in ink resistance. On the other hand, as for an ink flow path wall-forming material having a low swelling property to ink, it can be considered to be high in ink resistance. As above described (see, FIG. 1(d)), the ink flow path wall-forming material is applied to cover the relief solid layers (that is, the relief patterns), for example, by means of a dispenser. In the case where a plurality of ink pathways are intended to arrange at an increased density, it is necessary for the relief patterns to be miniatured in order to attain this purpose. In this case, the ink flow path wall-forming material is required to be of a low viscosity so that it can sufficiently get into spaces among those miniatured relief patterns. The use of an ink flow path wall-forming material having a low viscosity in this case is advantageous in that take-in of air bubble is hardly occurred upon the application of thereof. However, the relief patterns (that is, the relief solid layers), which serve to form a plurality of ink pathways, are usually formed of a positive type photoresist as above described. Thus, in the case where the ink flow path wall-forming material contains an organic solvent, the shapes of the relief solid layers are liable to deform because of the organic solvent, wherein precise ink pathways cannot be formed. Therefore, in order for the ink flow path wall-forming material to have a desired viscosity, it is desired to use an appropriate solvent-free material in the liquid state at room temperature and having a low viscosity and which is capable of being served as the ink flow path wall-forming material. In the prior art, epoxy resin has been used as the ink flow path wall-forming material since it excels in ink resistance and is in the liquid state at room temperature. The epoxy resin is corresponding to the foregoing ink flow path wall-forming material excelling in ink resistance but having a high elasticity modulus. In the case of an ink jet head having a plurality of ink flow path walls formed of epoxy resin, there is a problem in that the ink flow path walls are sometimes debonded from the substrate. Particularly, in the case of producing an ink jet head in which a plurality of energy generating elements are arranged at an increased density, the interval between each adjacent energy generating elements is remarkably shortened and because of this, the width of each ink flow path wall comprised of epoxy resin is necessary to be thinned accordingly. In this case, there entails a problem in that because the area of each ink flow path wall to be contacted with the substrate eventually becomes small, a sufficient adhesion is difficult to maintain between the ink flow path wall and the substrate. In addition to this, another problem entails in that because the epoxy resin is of a high elasticity modulus, a shrinkage stress effected upon hardening it cannot be sufficiently absorbed, often resulting a debonding between the ink flow path walls and the substrate. In order that the epoxy resin can absorb the foregoing shrinkage stress, the epoxy resin is necessary to be modified such that it has a reduced elasticity modulus. For this purpose, there can be considered a manner wherein the epoxy resin is replaced by a silicone-modified epoxy resin. However, the silicone-modified epoxy resin is remarkably low in elasticity modulus and because of this, there cannot be attained a desired bonding strength required for the ink flow path wall-forming material. In addition to this, the silicone-modified epoxy resin is insufficient in terms of mechanical strength. In this connection, the silicone-modified epoxy resin has never been used as a constituent material of an ink jet head. In order for the epoxy resin to have a reduced elasticity modulus, an appropriate flexibilizer is usually incorporated thereinto. By the way, in the field of using an ink jet system in recent years, as the printing medium, there have been used various printing members such as plastic sheets, fabrics and the like other than papers. Along with this, there is an increased demand for improving ink to be used in the ink jet system in terms of the color development and water resistance. In order to meet this demand, there is often used ink containing a slightly water-soluble dye or/and a pigment which is low in dispersion stability instead of the ordinary ink. However, to make full use of such dye and pigment cannot be attained in the case where the ordinary solvent is used. In order to solve this problem, there is a proposal of incorporating an alkali salt such as lithium hydroxide into the solvent to heighten the pH value of the ink (that is, to make the ink to be highly alkaline) whereby making full use of such dye and pigment. The results of experimental studies by the present inventors revealed that a conventional ink jet head having a plurality of ink flow path walls formed of an epoxy resin containing a flexibilizer is liable to provide prints accompanied by defects when it is operated using highly alkaline ink over a long period of time and wherein a debonding is liable to occur between the ink flow path walls and the substrate. This situation will be later detailed. SUMMARY OF THE INVENTION The present invention is aimed at resolving the foregoing problems found in the conventional ink jet head and providing an improved ink jet head capable of continuously performing stable ink discharging over a long period of time even in the case where highly alkaline ink is used. Another object of the present invention is to provide an improved ink jet head having a plurality of ink flow path walls excelling in ink resistance and which are not debonded from the substrate even when continuously used over a long period of time using highly alkaline ink. A further object of the present invention is to provide an improved, elongated ink jet head having a number of highly precise ink pathways arranged at an increased arrangement density. A further object of the present invention is to provide a highly reliable ink jet head which can be efficiently produced at a reduced production cost. An ink jet head according to the present invention which attains the above objects is alternatively defined in claim 1 and 15 and an ink jet apparatus using such an ink jet head is defined in claim 16. BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1(a), 1(b), 1(c), 1(d), 1(e) and 1(f) are schematic views for explaining the process of producing a conventional ink jet head. FIGs. 2(a), 2(a'), 2(b), 2(b'), 2(c), 2(c'), 2(d), 2(d'), 2(e), 2(e'), 2(f), 2(f'), 2(g), 2(g'), 2(h), 2(h'), 2(i), 2(i'), 2(j), and 2(j') are schematic views for explaining a process for producing an ink jet head according to the present invention. FIG. 3(a) is a schematic cross-sectional view of a discharging outlet portion of an ink jet head produced in each of Examples 1 and 2 which will be later described. FIG. 3(b) is a schematic cross-sectional view of a discharging outlet portion of an ink jet head produced in each of Comparative Examples 1 and 2 which will be later described. FIG. 4 is a schematically exploded view illustrating an example of the constitution of a conventional ink jet head. FIG. 5 is a schematic diagram of an ink jet apparatus in which an ink jet head according to the present invention can be installed. DESCRIPTION OF THE INVENTION AND THE PREFERRED EMBODIMENTS The present inventors made extensive studies in order to solve the foregoing problems in the prior art and in order to attain the foregoing objects. That is, the present inventors prepared a plurality of conventional ink jet heads having a plurality of ink flow path walls formed of a resin composition comprising epoxy resin incorporated with a flexibilizer. As for some of the ink jet heads, examination was made of its ink jet printing performance by continuously operating the ink jet head over a long period using the ordinary ink. As for the remaining ink jet heads, examination was made of its ink jet printing performance by continuously operating the ink jet head over a long period using highly alkaline ink containing a slightly water-soluble dye, a pigment and an alkali salt. In the case where the ordinary ink was used, any of the ink jet heads used was found to perform desirable printing over a long period of time. However, in the case where the highly alkaline ink was used, any of the ink jet heads used was found to sometimes provide prints accompanied by defects after the repeated use over a long period of time. As for each of the ink jet heads repeatedly operated over a long period of time wherein the highly alkaline ink, observation was made through its discharging outlet side. As a result, there was found occurrence of a debonding between the ink flow path walls and the substrate as for each of the ink jet heads. Based on the results obtained, the reason why the debonding was occurred between the ink flow path walls and the substrate in the case where the highly alkaline ink is considered due to the constituent resin of the ink flow path walls which is poor in resistance to the highly alkaline ink. Now, as above described, the epoxy resin as the main constituent of the resin composition by which the ink flow path walls are constituted excels in ink resistance. Therefore, it is considered that the debonding of the ink flow path walls from the substrate is chiefly due to the flexibilizer contained in the resin composition. In view of this, the present inventors made studies in order to find out an appropriate material capable of serving to reduce the elasticity modulus of the epoxy resin in the liquid state at room temperature which is conventionally used as the constituent material of the ink flow path walls in a conventional ink jet head, instead of the flexibilizer. As a result, there was obtained findings that when a given amount of an epoxy resin with a diepoxide structure having a siloxane bond (this epoxy resin will be hereinafter referred to as "siloxane bond possessing epoxy resin") is incorporated into a hardening epoxy resin in the liquid state at room temperature, there is provided a desirable resin composition in which the elasticity modulus of the hardening epoxy resin is reduced as desired and that the resin composition enables to form desirable ink flow path walls which excels in resistance to not only the ordinary ink but also the foregoing highly alkaline ink. The present invention has been accomplished based on these findings. The present invention provides an ink jet head including: a plurality of discharging outlets serving to discharge ink (hereinafter referred to as ink discharging outlet); a substrate for an ink jet recording head including a plurality of energy generating elements capable of generating an energy for discharging ink from said ink discharging outlets and wirings electrically connected to said energy generating elements; and a plurality of ink pathways each having an ink flow path wall of forming one of the ink pathways by joining to said substrate, characterized in that each of the ink flow path walls is constituted by (a) a specific epoxy resin composition which is in liquid state at room temperature, comprising (b) a hardening epoxy resin in the liquid state at room temperature as a main component and (c) a siloxane bond possessing epoxy resin (that is, an epoxy resin with a diepoxide structure having a siloxane bond) in a given amount. The epoxy resin composition will be hereinafter occasionally referred to as "ink flow path wall-forming material". The ink flow path walls formed of the above described specific resin composition (a) are apparently surpassing the conventional ink flow path walls comprised of the epoxy resin incorporated with the flexibilizer especially in terms of the resistance to not only the ordinary ink but also highly alkaline ink. Further, the specific resin composition (a) enables to form highly precise ink pathways which are surpassing those ink pathways formed of the epoxy resin incorporated with the flexibilizer. Particularly, the use of the siloxane bond possessing epoxy resin (c) in an amount equivalent to that of the flexibilizer incorporated into the epoxy resin effects to reduce the viscosity of the ink flow path wall-forming material (that is, the resin composition (a)) to a value corresponding to 1/10 of that of the epoxy resin incorporated with the flexibilizer, and no air bubble is taken into the resin composition (a) as the ink flow path wall-forming material upon the application thereof at the time of forming ink flow path walls. This situation makes it possible to form highly precise ink flow path walls without conducting deaeration. As above described, the ink flow path wall-forming material according to the present invention comprise the foregoing specific resin composition (a) (comprising a hardening epoxy resin (b) in the liquid state at room temperature as a main component and a siloxane bond possessing epoxy resin (c)). The resin composition (a) contains a curing agent or/and a polymerization initiator. If necessary, the resin composition (a) may contain a silane coupling agent capable of improving the adhesion of the resin composition. The hardening epoxy resin (b) in the liquid state at room temperature as the main component of the resin composition (a) means a hardening epoxy resin having a viscosity of 10 to 100,000 mPas (cps) at room temperature (25 °C). Thus, the hardening epoxy resin (b) can include hardening epoxy resins in the semisolid state at room temperature. As the hardening epoxy resin (b), any known hardening epoxy resins may be used as long as they have two or more epoxy groups in one molecule and are in the liquid state or the semisolid state at room temperature. Of these hardening epoxy resins, in the viewpoint of the ink resistance, those having a molecular weight of 300 or more have to be used in the present invention. Specific examples of the hardening epoxy resin (b) are bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol AD type epoxy resins, bisphenol AF type epoxy resins, and novolak type epoxy resins. These resins may be used either singly or in combination of two or more of them. The siloxane bond possessing epoxy resin (c) (that is, the epoxy resin with a diepoxide structure having a siloxane bond) used in the present invention may be epoxy resins obtained by a manner of reacting an appropriate compound having a Si-OH bond with epichlorohydrin in an alkaline aqueous solution or another manner of subjecting dimethyl polysiloxane having a Si-H group and a unsaturated epoxy compound such as acrylic glycidyl ether or vinylcyclohexane oxide to addition condensation in the presence of a platinum catalyst. It is possible to use any commercially available epoxy resins having a diepoxide structure with a siloxane bond such as 1,3-bis(3-glycidoxypropyl)tetramethyldisiloxane (trade name: B2405, produced by Chisso Kabushiki Kaisha). Those siloxane bond possessing epoxy resins having an excessively high molecular weight are not usable in the present invention because they are relatively high in viscosity and are low in ink resistance. And those silane bond possessing epoxy resins having an excessively small molecular weight are not usable in the present invention because they are of a low boiling point and cannot be stably maintained in the liquid state at room temperature. Specific example of the siloxane bond possessing epoxy resin (c) desirably usable in the present invention are those having the following structural formula (I) or (II). (wherein, each of R 1 to R 4 is an alkyl group of 1 to 4 carbon atoms, an alkenyl group of 2 to 6 carbon atoms, a phenyl group, or a substituted aromatic group wherein R 1 to R 4 may be the same or different one from the other; each of R 5 and R 6 is an alkylene group of 1 to 8 carbon atoms, or a phenylene group wherein R 5 and R 6 may be the same or different one from the other; n is an integer of 1 to 1000.) In the following, description will be made of an example of the production of an epoxy resin (c) having a diepoxide structure with a siloxane bond. Firstly, there is provided a reaction vessel equipped with an agitator, a temperature gage, a dropping funnel and a device capable of condensing and separating an azeotropic mixture of epichlorohydrin and water and returning an epichlorohydrin phase to the reaction vessel. Into the reaction vessel, a given amount of 1,1,3,3-tetramethyl-1,3-diethoxydisiloxane and a given amount of epichlorohydrin are introduced and the resultant mixture is circulated while stirring the mixture and while maintaining the mixture at a desired temperature. A given amount of an aqueous solution of NaOH is then dropwise added while maintaining the contents at a desired temperature. Then, of the water and epichlorohydrin distilled, only the epichlorohydrin phase is returned to the reaction vessel. After the addition of the NaOH aqueous solution has been completed, the excessive epichlorohydrin is recovered. Thereafter a given amount of toluene is added, followed by washing with water, wherein a salt caused and the residual alkali are removed. The resultant is subjected to treatment under a reduced pressure while heating, wherein the toluene and a by-product (ethylglycidyl ether) are removed. Thus, there is obtained a product comprising an epoxy resin having a diepoxide structure with a siloxane bond (1,1,3,3-tetramethyl-1,3-diglycidyletherdisiloxane). The main component of the resin composition (a), consisting of the hardening epoxy resin (b) in liquid state at room temperature and the siloxane bond possessing epoxy resin (c), contains according the present invention said siloxane bond possessing epoxy resin (c) in an amount of 10 to 40 wt.% versus the total amount of the hardening epoxy resin (b) and the siloxane bond possessing epoxy resin (c). In the case where the amount of the siloxane bond possessing epoxy resin (c) is less than 10 wt.%, the ink flow path wall-forming material is such that has a relatively high elasticity modulus, and because of this, the ink flow path wall-forming material cannot sufficiently absorb a shrinkage stress caused upon forming ink flow path walls. In an ink jet head having the resulting ink flow path walls thus formed, a debonding is liable to occur at the interface between the ink flow path walls and the substrate when the ink jet head is continuously operated over a long period of time using the foregoing highly alkaline ink. On the other hand, in the case where the amount of the siloxane bond possessing epoxy resin (c) is exceeding 40 wt.%, it takes a remarkable period of time until the ink flow path wall-forming material is hardened upon forming ink flow path walls, wherein a desired yield cannot be attained. In addition to this, the ink flow path walls formed of this ink flow path wall-forming material are insufficient in terms of the mechanical strength. Therefore, this ink flow path wall-forming material is not practically usable in the production of a desirable ink jet head. As the curing agent usable in the present invention, any of the conventional curing agents usually used in the case of curing an epoxy resin. Of these curing agents, amine series curing agents capable of causing curing at room temperature. Specific examples of such amine series curing agent are a commercially available modified aromatic amine series curing agent (trademark name: Fujicure FXK-830, produced by Fujikasei Kogyo Kabushiki Kaisha) and a commercially available modified aliphatic amine series curing agent (trademark name: Epomic Q614, produced by Mitsui Petrochemical Industries, Ltd.) The resin composition (a) (comprising the hardening epoxy resin (b) in the liquid state at room temperature as a main component and the siloxane bond possessing epoxy resin (c)) as the ink flow path wall-forming material in the present invention may be of a thermohardening type or a photo-hardening type. The resin composition (a) may be made to be of a photo-hardening type by incorporating an appropriate photo-curing agent into the resin composition. As such photo-curing agent, there can be mentioned cationic polymerized compounds which are not suffered from a polymerization hindrance due to oxygen, provide a slight cure shrinkage, provide an excellent adhesion and bonding property, and excel in heat resistance and resistance to chemicals. A preferred example of such cationic polymerized compound is a commercially available Adeka Optomer SP-170 (trademark name, produced by Asahi Denka Kogyo Kabushiki Kaisha). The resin composition (a) as the ink flow path wall-forming material is desired to contain a silane coupling agent. The resin composition (a) containing a silane coupling agent provides an improved adhesion and a reduced thixotropic property and is free of a problem of take-in of an air bubble upon applying onto a substrate. In addition, it exhibits a reduced viscosity. However, the silane coupling agent has a compatibility with a positive type photoresist, and because of this, the incorporation of an excessive amount of the silane coupling agent into the resin composition (a) shall be refrained. In addition to this, there is a tendency for the composition (a) to be decreased in terms of the ink resistance as the amount of the silane coupling agent to be incorporated into the resin composition (a) is increased. In view of this, it is desired for the amount of the silane coupling agent to be incorporated into the resin composition (a) to be in the range of 1 to 10 parts by weight versus the amount of the resin composition (a). As the silane coupling agent, it is desired to use epoxy series silane coupling agents in the viewpoint of their compatibility with the resin composition (a). In the case where the resin composition (a) contains an amine series thermohardening agent, it is desired to use an amine series silane coupling agent. In the following, description will be made of the the process of producing an ink jet head according to the present invention. FIGs. 2(a) through 2(j') are schematic views for explaining a process for producing an ink jet head according to the present invention. FIGs. 2(a), 2(b), 2(c), 2(d), 2(e), 2(f), 2(g), 2(h), 2(i), and 2(j) are schematic views of products obtained in respective steps in the production of an ink jet head when viewed from the discharging outlet side. FIGs. 2(a'), 2(b'), 2(c'), 2(d'), 2(e'), 2(f), 2(g'), 2(h'), 2(i'), and 2(j') are schematic slant views of the respective products shown in FIGs. 2(a) through 2(j). In this production example, there is described an ink jet head having three orifices. This is only for simplification purposes. It is a matter of course that the number of the orifices may be properly changed depending upon the kind of an ink jet head to be produced. In each figure, reference numeral 1 indicates a base member made of a material selected from the group consisting of silicon wafer, metals, glass, ceramics, and plastics. Now, on the base member 1, there are disposed a desired number of an energy generating element for generating an energy for discharging printing liquid (this energy generating element will be hereinafter referred to as liquid discharging energy generating element) such as an electrothermal converting element or piezoelectric element. FIGs. 2(a) and 2(a'), reference numeral 14 indicates an electrothermal converting element disposed on the base member 1. The electrothermal converting element 14 may be formed by the conventional thin film-forming technique employed in the semiconductor field. Particularly, the formation of the electrothermal converting element may be conducted, for example, in the following manner. That is, a heat generating resistor layer 11 comprised of, for example, HfB 2 , TaN, or Ta 2 O 5 is formed on the base member 1 by means of the sputtering or CVD process, followed by forming an electrode layer 12 comprised of, for example, Al on the heat generating resistor layer 11 by means of the sputtering, CVD or evaporation process. Thereafter, only the electrode layer 12 is patterned into such an electrode pattern as shown in FIG. 2(a') by means of the photolithography technique. Then, the heat generating resistor layer 11 is patterned into such a pattern as shown in FIG. 2(a') by means of the photolithography technique. By this, the formation of the electrothermal converting element 14 is completed. Herein, an exposed portion of the heat generating resistor layer 11 which is not covered by the electrode layer 12 corresponds an exothermic portion (a heat generating portion) 13. The liquid discharging energy generating element serves to generate an energy for discharging ink droplets thereby performing printing. In the case where the electrothermal converting element is used as the liquid discharging energy generating element, the electrothermal converting element serves to heat ink present in the vicinity thereof to cause a state change of volume expansion for the ink, resulting in discharging ink. On the other hand, in the case where the piezoelectric element is used as the liquid discharging energy generating element, ink discharging is conducted by virtue of a mechanical vibration caused by the piezoelectric element. In any case, wirings are electrically connected to any of these discharging energy generating elements (not shown in the figures). As for any of these discharging energy generating elements, in order to improve its durability, various functional layers including a protective layer are usually disposed thereon. In the present invention, these functional layers may be disposed. After the foregoing step (see, FIGs. 2(a) and 2(a')), a photosensitive resin layer 2 comprised of a positive type photoresist is disposed on the base member 1 so as to cover the liquid discharging energy generating elements disposed on the base member 1 (see, FIGs. 2(b) and 2(b')). This step shown in FIGs. 2(b) and 2(b') will be hereinafter referred to as second step. In a preferred embodiment, the photosensitive resin layer 2 is formed of a positive type photoresist capable of being resolved and removed in a later treatment. Specific examples of such photoresist are naphthoquinone series positive type photoresists, positive type photoresists of the chemical amplification type, and positive type photoresists of the backbone chain decomposition type. The formation of the photosensitive resin layer 2 may be conducted by means of the spin coating or roll coating technique. Other than this, it may be conducted by a manner of providing a dry film of any of the foregoing positive type photoresists and laminating the dry film on the base member 1. In a third step (see, FIGs. 2(c) and 2(c')), the photosensitive resin layer side of the stacked body obtained in the second step is subjected to light exposure through a patterning mask 3 for forming ink pathway-forming portions. FIGs. 2(d) and 2(d') are schematic views illustration the resultant obtained in this step in which portions 2' of the photosensitive resin layer 2 have been solubilized as a result of the light exposure. In a fourth step (see, FIGs. 2(e) and 2(e'), the light exposed portions 2' of the photosensitive resin layer 2 are subjected to development with an appropriate solvent such an alkali solution whereby forming a solid layer 4 (that is, a resist pattern) which serves to form ink pathways. The shapes of the ink pathways may be properly designed as desired by using, as the patterning mask 3, a patterning mask having a desired pattern capable of contributing to the formation such ink pathways. In this case, the resulting solid layer eventually becomes to have a pattern capable of providing such ink pathways having a desired shape. In this embodimment, as apparent from the figures, there are described three liquid discharging energy generating elements. Therefore, three ink discharging outlets are disposed to correspond the respective liquid discharging energy generating elements so that an ink droplet can be discharged from each of the ink discharging outlets. Further, there are described three ink pathways each corresponding to one of the three ink discharging outlets. The three ink pathways are communicated with a common ink chamber such that ink can be supplied from the common ink chamber to each of the three ink pathways. Now, in a fifth step (see, FIGs. 2(f) and 2(f')), in order to solubilize the solid layer 4, the entire of the solid layer is subjected to light exposure. The positive type resist constituting the solid layer is liable to produce nitrogen gas when it is reacted with light irradiated. Therefore, when an ink flow path wall-forming material 5 (see, FIGs. 2(g) and 2(g')) is disposed to cover the solid layer 4 without conducting any treatment for the solid layer, a problem will be sometimes occurred in that gas is taken into the ink flow path wall-forming material to result in deforming the shapes of ink pathways to be formed. In order to prevent occurrence of this problem, after the entire of the solid layer has been subjected to light exposure, it is desired for the solid layer to be subjected to deaeration treatment. In the case where a photo-curing material is used as the ink flow path wall-forming material 5, nitrogen gas will be sometimes caused from the solid layer 4 also upon subjecting the ink flow path wall-forming material to light exposure. Therefore, it is desired to make the solid layer 4 sufficiently reacted by alternately repeating a step of subjecting the entire of the solid layer to light exposure and a step of subjecting the solid layer to deaeration treatment. In a sixth step (see, FIGs. 2(g) and 2(g')), a hardening epoxy resin composition comprising a hardening epoxy resin in the liquid state at room temperature as a main component and an epoxy resin with a diepoxide structure having a siloxane bond (that is, the foregoing resin composition (a)) as the ink flow path wall-forming material 5 is applied onto the base member 1 so as to entirely cover the solid layer 4 formed on the base member by means of a dispenser or the like. Herein, after the application of the ink flow path wall-forming material 5, it is possible to join a top plate 7 to the ink flow path wall-forming material 5 applied. (see, FIGs. 2(h) and 2(h')). In a seventh step (see, FIGs. 2(i), 2(i'), 2(j) and 2(j')), the ink flow path wall-forming material 5 is subjected to heat treatment or light exposure treatment to harden the ink flow path wall forming material. Thereafter, the solid layer 4 is resolved and removed using an organic solvent such as halogen-containing hydrocarbon, ketone. ester, or alcohol or an aqueous alkaline solution of sodium hydroxide or potassium hydroxide to thereby form ink pathways and a common ink chamber in communication with any of these ink pathways. Thus, the production of an ink jet head is completed. In the following, description will be made of an example of an ink jet apparatus in which an ink jet head according to the present invention can be installed. FIG. 5 is an appearance perspective view illustrating an example of an ink jet apparatus (IJA) in which an ink jet head according to the present invention is installed as an ink jet head cartridge (IJC). In FIG. 5, reference numeral 20 indicates an ink jet head cartridge (IJC) provided with nozzle groups capable of discharging ink to the printing face of a printing sheet transported onto a platen 24. Reference numeral 16 indicates a carriage (HC) which serves to hold the IJC 20. The carriage HC is connected to a part of a driving belt 18 capable of transmitting a driving force such that it can be slidably moved together with two guide shafts 19A and 19B arranged in parallel with each other. By this, the IJC 20 is allowed to move back and forth along the entire of the printing sheet. Reference numeral 26 indicates a head restoring device which is disposed at one end of the moving passage of the IJC 20, specifically, at the position opposite the home position. The head restoring device 26 is operated by virtue of a driving force transmitted through a driving mechanism 23 from a motor 22, whereby capping the IJC 20. In relation to the capping for the IJC 20 by a cap member 26A of the head restoring device 26, the discharge restoration treatment of removing adhesive ink in the nozzles is conducted by way of ink sucking by means of an appropriate sucking means disposed in the head restoring device 26 or by way of ink pressure transportation by means of an appropriate pressurizing means whereby forcibly discharging the ink through the discharging outlets. When the printing is terminated, the IJC 20 is protected by capping it. Reference numeral 30 indicates a cleaning blade comprising a wiping member made of a silicon rubber which is arranged at a side face of the head restoring device 26. The cleaning blade 30 is supported by a blade supporting member 30A in a cantilever-like state. As well as in the case of the head restoring device 26, the cleaning blade 30 is operated by virtue of a driving force transmitted through the driving mechanism 23 from the motor 22, wherein the cleaning blade 30 is made capable of contacting with the discharging outlet face of the IJC 20. By this, the cleaning blade 30 is projected into the moving passage of the IJC 20 timely with the printing performance of the IJC 20 or after the discharge restoration treatment using the head restoring device 26 having been completed, to thereby remove dew drops, wettings, dirts, and the like deposited on the discharging outlet face of the IJC 20. The present invention provides prominent effects in an ink jet head or an ink jet apparatus, especially of the system in which printing is conducted by discharging utilizing thermal energy. As for the representative constitution and the principle, it is desired to adopt such fundamental principle as disclosed, for example, in U.S. Pat. No. 4,723,129 or U.S. Pat. No. 4,740,796. While this ink jet system is capable of applying either the so-called on-demand type or the continuous type, it is particularly effective in the case of the on-demand type because, by applying at least one driving for providing a rapid temperature rise exceeding nucleate boiling in response to printing information to an electrothermal converting element disposed for a sheet on which printing liquid (ink) is to be held or for a liquid pathway, the electrothermal converting element generates thermal energy to cause film boiling on a heat acting face of the ink jet head and as a result, a bubble can be formed in the printing liquid (ink) in a one-by-one corresponding relationship to such driving signal. By way of growth and contraction of the bubble, the printing liquid (ink) is discharged through a discharging outlet to form at least one droplet. It is more desirable to make the driving signal to be of a pulse shape, since in this case, growth and contraction of a bubble take place instantly and because of this, there can be attained discharging of the printing liquid (ink) excelling particularly in responsibility. As the driving signal of pulse shape, such driving signal as disclosed in U.S. Pat. No. 4,463,359 or U.S. Pat. No. 4,345,262 is suitable. Additionally, in the case where those conditions disclosed in U.S. Pat. No- 4,313,124, which relates to the invention concerning the rate of temperature rise at the heat acting face, are adopted, further improved printing can be conducted. As for the constitution of the ink jet head, the present invention includes, other than those constitutions of the discharging outlets, liquid pathways and electrothermal converting elements in combination (linear liquid flow pathway or perpendicular liquid flow pathway) which are disclosed in the above mentioned patent documents, the constitutions using such constitution in which a heat acting portion is disposed in a curved region as disclosed in U.S. Pat. No. 4,558,333 or U.S. Pat. No. 4,459,600. In addition, the present invention may effectively take a constitution based on the constitution in which a slit common to a plurality of electrothermal converting elements is used as a discharging portion of the electrothermal converting elements, which is disclosed in Japanese Unexamined Patent Publication No. 123670/1984 or another constitution in which an opening for absorbing a pressure wave of thermal energy is made to be corresponding to a discharging portion, which is disclosed in Japanese Unexamined Patent Publication No. 138461/1984. Further, the present invention is effective in the case of a full-line type ink jet head having a length corresponding to the maximum width of a printing medium on which printing can be performed. This full-line type ink jet head may be of such constitution in which those ink jet heads disclosed in the above mentioned patent documents are combined or such constitution in which they are integrated into a full-line head. The present invention is effective also in the case of an ink jet head of the exchangeable chip type wherein electric connection to an apparatus body or supply of ink from the apparatus body is enabled when it is mounted on the apparatus body or in the case of another ink jet head of the cartridge type wherein an ink tank is integrally disposed on the ink jet head itself. Further, it is desirable to add appropriate preparatory auxiliary means to an ink jet apparatus according to the present invention in view of further stabilizing the ink jet apparatus. Particularly, to employ preliminary heating means including an electrothermal converting element or a separate heating element or a combination of these and to employ a preparatory discharging mode in which discharging is conducted separately from printing are also effective in order to achieve stable printing. Further in addition, the present invention is extremely effective not only in an ink jet apparatus which as, as the printing mode, a printing mode of a main color such as black but also in an ink jet apparatus which includes a plurality of different colors or at least one of full-colors by color mixture, in which a ink jet head is integrally constituted or a plurality of ink jet heads are combined. In the above-described embodiments of the present invention, explanation has been made with the use of liquid ink. But in the present invention, it is possible to use such ink that is in the solid state at room temperature or other ink which becomes to be in the softened state at room temperature. In the foregoing ink jet apparatus, it is usual to adjust the temperature of ink itself to be in the range of 30 °C to 70 °C such that the viscosity of the ink lies in the range capable of being stably discharged. In view of this, any ink can be used as long as it is in the liquid state upon the application of a use printing signal. It is also possible to use those inks having a property of being liquefied, for the first time, with thermal energy, such that such ink can be liquefied and discharged in the liquid state upon the application of thermal energy depending upon a printing signal or other ink that can start its solidification beforehand at the time of its arrival at a printing member in order to prevent the temperature of the ink jet head from raising due to thermal energy purposely used as the energy for a state change of ink from solid state to liquid state or in order to prevent ink from being vaporized by solidifying the ink in a state of being allowed to stand. In the case of using these inks, they can be used in such a manner as disclosed in Japanese Unexamined Patent Publication No. 56847/1985 or Japanese Unexamined Patent Publication No. 71260/1985 in which ink is maintained in concaved portions or penetrations of a porous sheet in the liquid state or in the solid state and the porous sheet is arranged to provide a configuration opposite the electrothermal converting element. In the present invention, it is the most effective to conduct the foregoing film boiling manner for each of the above described inks. Experiments In the following, experiments are discribed which were conducted by the present inventors in order to accomplish the present invention. In view of the problems found in the conventional ink jet head in that the ink flow path walls are liable to debond from the substrate when the ink jet head is continuously operated over a long period of time using a highly alkaline ink, the present inventors conducted experimental studies in order to find out a desirable ink flow path wall-forming material having a desired elasticity modulus and an excellent ink resistance. Particularly, as for the foregoing epoxy resin composition (a) comprising (b) a hardening epoxy resin in the liquid state at room temperature as a main component and (c) a siloxane bond possessing epoxy resin (that is, an epoxy resin with a diepoxide structure having a siloxane bond) which has the advantages of the hardening epoxy resin and a desired elasticity modulus and which exhibits an excellent ink resistance which was developed by the present inventors, experimental studied were conducted of whether or not the epoxy resin composition (a) is effectively usable as the ink flow path wall-forming material so that the problems in the conventional ink jet head can be solved through the under described Experiments 1 to 22. In each of the following Experiments 1 to 22, an ink flow path wall-forming material was prepared and the resultant ink flow path wall-forming material was evaluated with respect to ink resistance and elasticity modulus in order to examine whether or not it is effective in forming desirable ink flow path walls which are free of the above problems. Experiment 1 As the hardening epoxy resin (b) in the liquid state at room temperature, there was provided bisphenol A type epoxy resin (trademark name: Epikote 828, produced by Yuka Shell Kabushiku Kaisha). This bisphenol A type epoxy resin in an amount of 75 parts by weight was well mixed with 25 parts by weight of 1,3-bis(3-glycidoxypropyl) tetramethyldisiloxane as the siloxane bond possessing epoxy resin (c). Thus, there was obtained a main component. 100 parts of weight of the main component was mixed with 50 parts by weight of a modified aromatic amine series curing agent comprising Fujicure FXK-830 (trademark mama, produced by Fujikasei Kogyo Kabushiki Kaisha). Then, to the resultant, 5 parts by weight of an epoxy series silane coupling agent A-187 (trade name, produced by Nippon Unicar Kabushiki Kaisha) was added, and the mixture obtained was homogenized. Thus, there was obtained a specimen in the liquid state at room temperature (hereinafter referred to as Sample A). Experiment 2 As the hardening epoxy resin (b) in the liquid state at room temperature, there was provided bisphenol A type epoxy resin (trademark name: Epikote 828, produced by Yuka Shell Kabishiki Kaisha). This bisphenol A type epoxy resin in an amount of 75 parts by weight was well mixed with 25 parts by weight of 1,1,3,3-tetramethyl-1,3-diglycidyletherdisiloxane as the siloxane bond possessing epoxy resin (c). Thus, there was obtained a main component. 100 parts of weight of the main component was mixed with 28 parts by weight of a modified aliphatic amine series curing agent comprising Epomic Q614 (trademark name, produced by Mitsui Petrochemical Industries, Ltd.). Then, to the resultant, 5 parts by weight of an epoxy series silane coupling agent A-187 (trade name, produced by Nippon Unicar Kabushiki Kaisha) was added, and the mixture obtained was homogenized. Thus, there was obtained a specimen in the liquid state at room temperature (hereinafter referred to as Sample B). Experiment 3 As the hardening epoxy resin (b) in the liquid state at room temperature, there was provided bisphenol AD type epoxy resin (trademark name: Epomic R710, produced by Mitsui Petrochemical Industries, Ltd.). This bisphenol AD type epoxy resin in an amount of 90 parts by weight was well mixed with 10 parts by weight of 1,3-bis(3-glycidoxypropyl)tetramethyldisiloxane as the siloxane bond possessing epoxy resin (c). Thus, there was obtained a main component. 100 parts of weight of the main component was mixed with 28 parts by weight of a modified aliphatic amine series curing agent comprising Epomic Q614 (trademark name, produced by Mitsui Petrochemical Industries, Ltd.). Then, to the resultant, 5 parts by weight of an epoxy series silane coupling agent A-187 (trade name, produced by Nippon Unicar Kabushiki Kaisha) was added, and the mixture obtained was homogenized. Thus, there was obtained a specimen in the liquid state at room temperature (hereinafter referred to as Sample C). Experiment 4 As the hardening epoxy resin (b) in the liquid state at room temperature, there was provided bisphenol AD type epoxy resin (trademark name: Epomic R710, produced by Mitsui Petrochemical Industries, Ltd.). This bisphenol AD type epoxy resin in an amount of 90 parts by weight was well mixed with 10 parts by weight of 1,1,3,3-tetramethyl-1,3-diglycidyletherdisiloxane as the siloxane bond possessing epoxy resin (c). Thus, there was obtained a main component. 100 parts of weight of the main component was mixed with 50 parts by weight of a modified aromatic amine series curing agent comprising Fujicure FXK830 (trademark name, produced by Fujikasei Kabushiki Kaisha). Then, to the resultant, 5 parts by weight of an epoxy series silane coupling agent A-187 (trade name, produced by Nippon Unicar Kabushiki Kaisha) was added, and the mixture obtained was homogenized. Thus, there was obtained a specimen in the liquid state at room temperature (hereinafter referred to as Sample D). Experiment 5 (not according to the invention) The procedures of Experiment 1 were repeated, except that the amount of the bisphenol A type epoxy resin was changed to 95 parts by weight and the amount of the 1,3-bis(3-glycidoxypropyl)tetramethyldisiloxane was changed to 5 parts by weight, to thereby obtain a specimen in the liquid state at room temperature (hereinafter referred to as Sample E). Experiment 6 The procedures of Experiment 1 were repeated, except that the amount of the bisphenol A type epoxy resin was changed to 85 parts by weight and the amount of the 1,3-bis(3-glycidoxypropyl)tetramethyldisiloxane was changed to 15 parts by weight, to thereby obtain a specimen in the liquid state at room temperature (hereinafter referred to as Sample F). Experiment 7 The procedures of Experiment 1 were repeated, except that the amount of the bisphenol A type epoxy resin was changed to 65 parts by weight and the amount of the 1,3-bis(3-glycidoxypropyl)tetramethyldisiloxane was changed to 35 parts by weight, to thereby obtain a specimen in the liquid state at room temperature (hereinafter referred to as Sample G). Experiment 8 The procedures of Experiment 1 were repeated, except that the amount of the bisphenol A type epoxy resin was changed to 60 parts by weight and the amount of the 1,3-bis(3-glycidoxypropyl)tetramethyldisiloxane was changed to 40 parts by weight, to thereby obtain a specimen in the liquid state at room temperature (hereinafter referred to as Sample H). Experiment 9 (not according to the invention) The procedures of Experiment 1 were repeated, except that the amount of the bisphenol A type epoxy resin was changed to 50 parts by weight and the amount of the 1,3-bis(3-glycidoxypropyl)tetramethyldisiloxane was changed to 50 parts by weight, to thereby obtain a specimen in the liquid state at room temperature (hereinafter referred to as Sample I). Experiment 10 (not according to the invention) As the hardening epoxy resin (b) in the liquid state at room temperature, there was provided bisphenol AD type epoxy resin (trademark name: Epomic R710, produced by Mitsui Petrochemical Industries, Ltd.). This bisphenol AD type epoxy resin in an amount of 95 parts by weight was well mixed with 5 parts by weight of 1,1,3,3-tetramethyl-1,3-diglycidyletherdisiloxane as the siloxane bond possessing epoxy resin (c). Thus, there was obtained a main component. 100 parts of weight of the main component was mixed with 28 parts by weight of a modified aliphatic amine series curing agent comprising Epomic Q614 (trademark name, produced by Mitsui Petrochemical Industries, Ltd.). Then, to the resultant, 5 parts by weight of an epoxy series silane coupling agent A-187 (trade name, produced by Nippon Unicar Kabushiki Kaisha) was added, and the mixture obtained was homogenized. Thus, there was obtained a specimen in the liquid state at room temperature (hereinafter referred to as Sample J). Experiment 11 The procedures of Experiment 10 were repeated, except that the amount of the bisphenol AD type epoxy resin was changed to 90 parts by weight and the amount of the 1,1,3,3-tetramethyl-1,3-diglycidyletherdisiloxane was changed to 10 parts by weight, to thereby obtain a specimen in the liquid state at room temperature (hereinafter referred to as Sample K). Experiment 12 The procedures of Experiment 10 were repeated, except that the amount of the bisphenol AD type epoxy resin was changed to 60 parts by weight and the amount of the 1,1,3,3-tetramethyl-1,3-diglycidyletherdisiloxane was changed to 40 parts by weight, to thereby obtain a specimen in the liquid state at room temperature (hereinafter referred to as Sample L). Experiment 13 (not according to the invention) The procedures of Experiment 1 were repeated, except that the amount of the bisphenol A type epoxy resin was changed to 100 parts by weight, to thereby obtain a specimen in the liquid state at room temperature (hereinafter referred to as Sample M). Experiment 14 (not according to the invention) As the hardening epoxy resin (b) in the liquid state at room temperature, there was provided bisphenol A type epoxy resin (trademark name: Epikote 828, produced by Yuka Shell Kabushiki Kaisha). This bisphenol A type epoxy resin in an amount of 75 parts by weight was well mixed with 25 parts by weight of a flexibilizer Epolite 3002 (trademark name, produced by Kyoeiyushi Kabushiki Kaisha). Thus, there was obtained a main component. 100 parts of weight of the main component was mixed with 50 parts by weight of a modified aromatic amine series curing agent comprising Fujicure FXK-830 (trademark name, produced by Fujikasei Kogyo Kabushiki Kaisha). Then, to the resultant, 5 parts by weight of an epoxy series silane coupling agent A-187 (trade name, produced by Nippon Unicar Kabushiki Kaisha) was added, and the mixture obtained was homogenized. Thus, there was obtained a specimen in the liquid state at room temperature (hereinafter referred to as Sample N). Experiment 15 As the hardening epoxy resin (b) in the liquid state at room temperature, there was provided bisphenol A type epoxy resin (trademark name: Epikote 828, produced by Yuka Shell Kabishiki Kaisha). This bisphenol A type epoxy resin in an amount of 75 parts by weight was well mixed with 25 parts by weight of 1,3-bis(3-glycidoxypropyl)tetramethyldisiloxane as the siloxane bond possessing epoxy resin (c). Thus, there was obtained a main component. 100 parts of weight of the main component was mixed with 1.5 parts by weight of a cationic ultraviolet-ray curing initiator Adeka Optomer SP-170 (trademark name, produced by Asahidenka Kogyo Kabushiki Kaisha). Then, to the resultant, 5 parts by weight of an epoxy series silane coupling agent A-187 (trade name, produced by Nippon Unicar Kabushiki Kaisha) was added, and the mixture obtained was homogenized. Thus, there was obtained a specimen in the liquid state at room temperature (hereinafter referred to as Sample O). Experiment 16 As the hardening epoxy resin (b) in the liquid state at room temperature, there was provided bisphenol AD type epoxy resin (trademark name: Epomic R710, produced by Mitsui Petrochemical Industries, Ltd.). This bisphenol AD type epoxy resin in an amount of 80 parts by weight was well mixed with 20 parts by weight of 1,1,3,3-tetramethyl-1,3-diglycidyletherdisiloxane as the siloxane bond possessing epoxy resin (c). Thus, there was obtained a main component. 100 parts of weight of the main component was mixed with 1.5 parts by weight of a cationic ultraviolet-ray curing initiator Adeka Optomer SP-170 (trademark name, produced by Asahidenka Kogyo Kabushiki Kaisha). Then, to the resultant, 5 parts by weight of an epoxy series silane coupling agent A-187 (trade name, produced by Nippon Unicar Kabushiki Kaisha) was added, and the mixture obtained was homogenized. Thus, there was obtained a specimen in the liquid state at room temperature (hereinafter referred to as Sample P). Experiment 17 (not according to the invention) As the hardening epoxy resin (b) in the liquid state at room temperature, there was provided bisphenol A type epoxy resin (trademark name: Epikote 828, produced by Yuka Shell Kabushiki Kaisha). This bisphenol A type epoxy resin in an amount of 95 parts by weight was well mixed with 5 parts by weight of 1,1,3,3-tetramethyl-1,3-diglycidyletherdisiloxane as the siloxane bond possessing epoxy resin (c). Thus, there was obtained a main component. 100 parts of weight of the main component was mixed with 1.5 parts by weight of a cationic ultraviolet-ray curing initiator Adeka Optomer SP-170 (trademark name, produced by Asahidenka Kogyo Kabushiki Kaisha). Then, to the resultant, 5 parts by weight of an epoxy series silane coupling agent A-187 (trade name, produced by Nippon Unicar Kabushiki Kaisha) was added, and the mixture obtained was homogenized. Thus, there was obtained a specimen in the liquid state at room temperature (hereinafter referred to as Sample Q). Experiment 18 As the hardening epoxy resin (b) in the liquid state at room temperature, there was provided bisphenol AD type epoxy resin (trademark name: Epomic R710, produced by Mitsui Petrochemical Industries, Ltd.). This bisphenol AD type epoxy resin in an amount of 90 parts by weight was well mixed with 10 parts by weight of 1,3-bis(3-glycidoxypropyl)tetramethyldisiloxane as the siloxane bond possessing epoxy resin (c). Thus, there was obtained a main component. 100 parts of weight of the main component was mixed with 1.5 parts by weight of a cationic ultraviolet-ray curing initiator Adeka Optomer SP-170 (trademark name, produced by Asahidenka Kogyo Kabushiki Kaisha). Then, to the resultant, 5 parts by weight of an epoxy series silane coupling agent A-187 (trade name, produced by Nippon Unicar Kabushiki Kaisha) was added, and the mixture obtained was homogenized. Thus, there was obtained a specimen in the liquid state at room temperature (hereinafter referred to as Sample R). Experiment 19 The procedures of Experiment 15 were repeated, except that the amount of the bisphenol A type epoxy resin was changed to 60 parts by weight and the amount of the 1,3-bis(3-glycidoxypropyl)tetramethyldisiloxane was changed to 40 parts by weight, to thereby obtain a specimen in the liquid state at room temperature (hereinafter referred to as Sample S). Experiment 20 (not according to the invention) The procedures of Experiment 16 were repeated, except that the amount of the bisphenol AD type epoxy resin was changed to 50 parts by weight and the amount of the 1,1,3,3-tetramethyl-1,3-diglycidyletherdisiloxane was changed to 50 parts by weight, to thereby obtain a specimen in the liquid state at room temperature (hereinafter referred to as Sample T). Experiment 21 (not according to the invention) The procedures of Experiment 15 were repeated, except that the amount of the bisphenol A type epoxy resin was changed to 100 parts by weight, to thereby obtain a specimen in the liquid state at room temperature (hereinafter referred to as Sample U). Experiment 22 (not according to the invention) The procedures of Experiment 14 were repeated, except that the modified aromatic amine series curing agent comprising Fujicure FXK-830 was replaced by a cationic ultraviolet-ray curing initiator Adeka Optomer SP-170 (trademark name, produced by Asahidenka Kogyo Kabushiki Kaisha) and 1.5 parts by weight of this cationic ultraviolet-ray curing initiator was mixed with 100 parts of the main component, to thereby obtain a specimen in the liquid state at room temperature (hereinafter referred to as Sample V). As for each of Samples A to V obtained in Experiments 1 to 22, evaluation was conducted with respect to adhesion (or bonding property) and form retention in order to examine its ink resistance and elasticity modulus which are required for it being usable as an ink flow path wall-forming material capable of forming high quality ink flow path walls. The evaluation of each evaluation item was conducted in the following manner. Evaluation of adhesion (bonding property): Each of Samples A to V was evaluated with respect to ink resistance, adhesion (bonding property) and elasticity modulus in the following manner. That is, as for each sample, there were provided two glass plates as a substrate. And on the surface of each substrate, a 100 um thick coat was formed by applying a specimen of each sample. Then, as for each of Samples A to N, preparatory hardening was conducted at room temperature, followed by conducting thermal hardening (thermosetting) at 130 °C for 2 hours. As for each of Samples O to V, irradiation of ultraviolet rays of 8.3J was firstly conducted, followed by conducting thermal hardening (thermosetting) at 130 °C for an hour. The two substrates each having a hardened film thereon as for each of Samples A to V were treated as follows. (i) One substrate was immersed in the ordinary ink (comprising 36 wt.% of DEG and 74 wt.% of water), wherein it was allowed to stand under conditions of 120 °C and 2 atmospheric pressure for 10 hours. Thereafter, the substrate was taken out from the ink, and it was washed with water, followed by drying. (ii) The other substrate was immersed in highly alkaline ink of pH 10.7 (comprising 10.0 wt.% of GLY, 5.0 wt.% of UREA, 5.0 wt.% of IPA, 0.4 wt% of lithium hydroxide, 0.5 wt.% of ammonium sulfate, and 79.9 wt.% of water), wherein it was allowed to stand under conditions of 120 °C and 2 atmospheric pressure for 10 hours. Thereafter, the substrate was taken out from the ink, and it was washed with water, followed by drying. Each of the two resultants obtained in the above treatments (i) and (ii) was examined whether or not a debonding was present at the hardened film on the substrate by means of a microscope. The examined results obtained are collectively shown in Table 1 based on the following criteria. ○ : the case wherein no debonding was found at the hardened film; and X : the case wherein apparent debonding was found at the hardened film. Now, it is considered that when the hardened film on the substrate is not satisfactory in terms of either the ink resistance or elasticity modulus, a debonding is caused at the hardened film. Therefore, it can be said that the hardened film on the substrate accompanied by no debonding is satisfactory in terms of both the ink resistance and elasticity modulus. Evaluation of form retention: In the above evaluation of adhesion (bonding property), the hardened film which is excessively high in elasticity modulus can be distinguished, but as for the hardened film which is excessively low in elasticity modulus, it cannot be distinguished. As for such hardened film which is excessively low in elasticity modulus, when it is used in forming an ink pathway, the ink pathway formed is liable to deform when it is suffered from an external pressure, because it is insufficient in terms of the mechanical strength. In view of this, as for each of Samples A to V, evaluation was conducted with respect to form retention. This evaluation was conducted by way of the bending elasticity modulus test in the following manner. That is, in accordance with the test method of JIS-K-6911, a specimen of each of Samples A to V was casted into a mold, followed by hardening. As for each of Samples A to N, the hardening was conducted in the following manner. That is, preparatory hardening was conducted at room temperature, followed by conducting thermal hardening (thermosetting) at 130 °C for 2 hours. As for each of Samples O to V, the hardening was conducted in the following manner. That is, irradiation of ultraviolet rays of 8.3J was firstly conducted, followed by conducting thermal hardening (thermosetting) at 130 °C for an hour. Thus, there was obtained a molded product (hereinafter referred to as solid sample) as for each of Samples A to V. Each solid sample thus obtained was set to a commercially available bending modulus elasticity measuring instrument RTM-100 (trademark name, produced by Toyo Baldwin Kabushiki Kaisha) to examine its bending elasticity modulus. The results obtained are collectively shown in Table 1 based on the following criteria. ○ : the case wherein the solid sample was 60 kgf/mm 2 or more in bending elasticity modulus; and X : the case wherein the solid sample was less than 60 kgf/mm 2 in bending elasticity modulus. Herein, the form retention means the mechanical strength of a material when it is used as a constituent of an ink jet head. When the material is less than 60 kgf/mm 2 in bending elasticity modulus, it can be said that the material is insufficient in terms of the mechanical strength and therefore, when ink flow path walls are formed using this material, the ink flow path walls are poor in form retention, and they are liable to be suffered from a damage. In addition, evaluation was conducted based on the evaluated results with respect to adhesion (bonding property) and form retention. The results obtained are collectively shown in Table 1 based on the following criteria. ○ : the case wherein both the evaluated result with respect to adhesion (bonding property) and the evaluated result with respect to form retention are excellent; and X : the case wherein either the evaluated result with respect to adhesion (bonding property) or the evaluated result with respect to form retention is inferior. Total Evaluation From the evaluated results with respect to adhesion (bonding property), there were obtained the following findings. That is, the hardened film formed of any of Samples E, J, M, Q and U obtained in Experiments 5, 10, 13, 17 and 21 causes a debonding when immersed in the ordinary ink and in the highly alkaline ink wherein it is peeled off from the substrate. As for the hardened film formed of any of Samples N and V obtained in Experiments 14 and 22, although it does not causes a debonding when immersed in the ordinary ink, when it is immersed in the highly alkaline ink, it causes a debonding wherein it is peeled off from the substrate. As for the hardened film formed of Sample F, it is substantially free of occurrence of a debonding when immersed in the ordinary ink and also in the highly alkaline ink, but when immersed in the highly alkaline ink, a slight removal is occurred between the hardened film and the substrate. As for the hardened film formed of each of the remaining samples, no debonding is occurred when immersed in the ordinary ink and also in the highly alkaline ink. From the evaluated results with respect to form retention, there were obtained the following findings. That is, the molded product obtained from each of Samples I and T obtained in Experiments 9 and 20 is less than 60 kgf/mm 2 in bending elasticity modulus and thus, it is inferior in mechanical strength. Based on the above findings, as for the hardened film formed of each of Samples E, J, M, Q and U obtained in Experiments 5, 10, 13, 17 and 21, the reason why the hardened film causes a debonding when immersed in the ordinary ink and also in the highly alkaline ink is considered due to a fact that because the main component is relatively high in elasticity modulus, specifically, the content of the hardening epoxy resin (b) in the main component is relatively high, a shrinkage stress generated upon the hardening cannot be sufficiently absorbed to result in causing such debonding wherein the hardened film is peeled off from the substrate. Similarly, as for the hardened film formed of each of Samples N and V obtained in Experiments 14 and 22, the reason why the hardened film causes a debonding when immersed in the highly alkaline ink is considered due to a fact that the flexibilizer is decomposed with the action of the highly alkaline ink to reduce the ink resistance of the hardened film whereby causing such debonding wherein the hardened film is peeled off from the substrate. As for the reason why the molded product formed from each of Samples I and T obtained in Experiments 9 and 20 is inferior in mechanical strength, it is considered due to a fact that the content of the hardening epoxy resin (b) in the main component is relatively small and this makes the molded product to be inferior in mechanical strength. In addition, each of Samples I and T obtained in Experiments 9 and 20 takes a remarkably longer period of time upon the hardening in comparison with the hardening time in the case of each of other samples. Therefore, there cannot be attained a desired yield in the production of an ink jet head by using any of Samples I and T. Separately, as Sample 0 obtained in Experiment 15 (composed of 25 parts by weight of bisphenol A type epoxy resin, 25 parts by weight of 1,3-bis(3-glycidoxypropyl)tetramethyldisiloxane, and 1.5 parts by weight of a cationic ultraviolet-ray curing initiator) and Sample V obtained in Experiment 22 (composed of 25 parts by weight of bisphenol A type epoxy resin, 25 parts by weight of the conventional flexibilizer (Epolite 3002), and 1.5 parts by weight of a cationic ultraviolet-ray curing initiator), their viscosity was measured. As a result, the viscosity of the former sample was found to be 340 cps and that of the latter sample was found to be 4500 cps. From these results, it is understood that the former sample is of a remarkably low viscosity corresponding to a value of about 1/13 of the viscosity of the latter sample (in which the conventional flexibilizer was used) and that the former sample is free of a problem of causing take-in of an air bubble upon the application thereon onto a substrate but the latter sample is not free of such problem. From the above description, it is understood that any of Samples A, B, C, D, F, G, H, K, L, O, P, R, and S (each comprising the foregoing resin composion (a) as the main component, said resin composition comprising the hardening epoxy resin (b) in the liquid state at room temperature and the diepoxide structure possessing epoxy resin (c)) obtained in Experiments 1-4, 6-8, 11-12, 15-16, and 18-19 belonging to the present invention is desirably usable as an ink flow path wall-forming material which enables to form high quality ink flow path walls free from occurrence of a debonding even in the case of using a highly alkaline ink, resulting in making it possible to efficiently produce a high quality ink jet head which ensures stable ink discharging. Of these samples belonging to the present invention, Samples A, B, O and P obtained in Experiments 1, 2, 15 and 16 are the most desirable in the total viewponts. The present invention will be described in more detail by reference to the following examples, which are provided here for illustrative purposes only and are not intended to limit the scope of the present invention. In the following, there will be described an example in which Sample A obtained in Experiment 1 is used and an example in Sample P obtained in Example 16 is used. There will be also described a comparative example in which Sample M obtained in Experiment 13 is used and a comparative example in which Sample N obtained in Experiment 14 is used. Example 1 There was provided a silicon wafer as a base member. On the surface of the base member, a 2000 A thick HfB 2 layer as a heat generating resistor layer was formed by means of the sputtering process, followed by forming, on the heat generating resistor layer, a 1 µm thick aluminum layer as an electrode layer by means of the electron beam evaporation process. The base member having the heat generating resistor layer and electrode layer formed thereon was subjected to patterning by means of the photolithography technique to form a plurality of electrothermal converting elements at 360 dpi corresponding to 128 nozzles. Then, onto the base member, a positive type photoresist PMER AR-900 (trademark name, produced by Tokyo Ohkakogyo Kabushiki Kaisha) was applied in an amount to provide a thickness of 30 um when dried so as to entirely cover the electrothermal converting elements on the base member by means of the spin coating process, followed by conducting baking treatment at 90 °C for 40 minutes in an oven, whereby forming a resist layer. Successively, the resultant was subjected to light exposure using a nozzle patterning mask, followed by subjecting to development and then to rinsing, whereby forming a patterned solid layer having a nozzle pattern with a pitch of 40 µm. The resin composition comprising Sample A obtained in Experiment 1 was applied onto the base member so as to entirely cover the solid layer, followed by subjecting to preliminary hardening treatment at 25 °C for 24 hours and then to thermal hardening treatment (thermosetting treatment) at 100 °C for 2 hours. The resultant was immersed in an aqueous solution of sodium hydroxide with a 3 wt.% content, wherein the solid layer having the nozzle pattern was removed. By this, an ink jet head was obtained. In this way, there were prepared a plurality of ink jet heads. Each of the resultant ink jet heads was subjected to continuous printing test, wherein printing was continuously conducted for 1000 hours using highly alkaline ink of pH 10.7 (composed of 10.0 wt.% of GLY, 5.0 wt.% of urea, 5.0 wt.% of IPA, 0.4 wt.% of lithium hydroxide, 0.5 wt.% of ammonium sulfate, and 79.9 wt.% of water). As a result, any of the ink jet heads was found to conduct desirable printing stably and continuously over the period of 1000 hours without causing any defective ink discharge and any defective print. As for each ink jet head having been subjected to the continuous printing test, observation was conducted its portions in the vicinity of the discharging outlets. As a result, it was found that the interface between the base member (that is, the substrate for an ink jet head) and the ink flow path walls is maintained in a desirably bonded state with no removal as shown in FIG. 3(a). Example 2 There was provided a silicon wafer as a base member. On the surface of the base member, a 2000 Å thick HfB 2 layer as a heat generating resistor layer by means of the sputtering process, followed by forming, on the heat generating resistor layer, a 1 µm thick aluminum layer as an electrode layer by means of the electron beam evaporation process. The base member having the heat generating resistor layer and electrode layer formed thereon was subjected to patterning by means of the photolithography technique to form a plurality of electrothermal converting elements at 360 dpi corresponding to 128 nozzles. Then, onto the base member, a positive type photoresist PMER AR-900 (trademark name, produced by Tokyo Ohkakogyo Kabushiki Kaisha) was applied in an amount to provide a thickness of 30 um when dried so as to entirely cover the electrothermal converting elements on the base member by means of the spin coating process, followed by conducting baking treatment at 90 °C for 40 minutes in an oven, whereby forming a resist layer. Successively, the resultant was subjected to light exposure using a nozzle patterning mask, followed by subjecting to development and then to rinsing, whereby forming a patterned solid layer having a nozzle pattern with a pitch of 40 µm. The resin composition comprising Sample P obtained in Experiment 16 was applied onto the base member so as to entirely cover the solid layer, followed by subjecting to irradiation of ultraviolet rays of 8.3J and then to thermal hardening treatment (thermosetting treatment) at 130 °C for an hour. The resultant was immersed in an aqueous solution of sodium hydroxide with a 3 wt.% content, wherein the solid layer having the nozzle pattern was removed. By this, an ink jet head was obtained. In this way, there were prepared a plurality of ink jet heads. Each of the resultant ink jet heads was subjected to continuous printing test, wherein printing was continuously conducted for 1000 hours using highly alkaline ink of pH 10.7 (composed of 10.0 wt.% of GLY, 5.0 wt.% of urea, 5.0 wt.% of IPA, 0.4 wt.% of lithium hydroxide, 0.5 wt.% of ammonium sulfate, and 79.9 wt.% of water). As a result, any of the ink jet heads was found to conduct desirable printing stably and continuously over the period of 1000 hours without causing any defective ink discharge and any defective print. As for each ink jet head having been subjected to the continuous printing test, observation was conducted its portions in the vicinity of the discharging outlets. As a result, it was found that the interface between the base member (that is, the substrate for an ink jet head) and the ink flow path walls is maintained in a desirably bonded state with no removal as shown in FIG. 3(a). Comparative Example 1 The procedures of Example 1 were repeated, except that Sample M obtained in Experiment 13 was used as the ink flow path wall-forming material for an ink jet head, to thereby obtain a plurality of comparative ink jet heads. Each of the resultant comparative ink jet heads was subjected to continuous printing test, wherein printing was continuously conducted for 1000 hours using highly alkaline ink of pH 10.7 (composed of 10.0 wt.% of GLY, 5.0 wt.% of urea, 5.0 wt.% of IPA, 0.4 wt.% of lithium hydroxide, 0.5 wt.% of ammonium sulfate, and 79.9 wt.% of water). As a result, any of the comparative ink jet heads was found to often cause non-ink discharging and provision of defective prints. As for each comparative ink jet head having been subjected to the continuous printing test, observation was conducted its portions in the vicinity of the discharging outlets. As a result, it was found that the ink flow path walls are debonded from the base member (that is, the substrate for an ink jet head) as shown in FIG. 3(b). Comparative Example 2 The procedures of Example 1 were repeated, except that Sample N obtained in Experiment 14 was used as the ink flow path wall-forming material for an ink jet head, to thereby obtain a plurality of comparative ink jet heads. Each of the resultant comparative ink jet heads was subjected to continuous printing test, wherein printing was continuously conducted for 1000 hours using highly alkaline ink of pH 10.7 (composed of 10.0 wt.% of GLY, 5.0 wt.% of urea, 5.0 wt.% of IPA, 0.4 wt.% of lithium hydroxide, 0.5 wt.% of ammonium sulfate, and 79.9 wt.% of water). As a result, any of the comparative ink jet heads was found to often cause non-ink discharging and provision of defective prints. As for each comparative ink iet head having been subjected to the continuous printing test, observation was conducted its portions in the vicinity of the discharging outlets. As a result, it was found that the ink flow path walls are debonded from the base member (that is, the substrate for an ink jet head) as shown in FIG. 3(b). From the above described results, it is understood that the foregoing resin composition (a) according to the present invention (comprising the foregoing hardening epoxy resin (b) in the liquid state at room temperature as a main component and the foregoing specific siloxane bond possessing epoxy resin (c)) enables to form high quality ink flow path walls for an ink jet head which are free from occurrence of a debonding from the substrate even in the case of using highly alkaline ink and that an ink jet head having the high quality ink flow path walls excels in ink discharging performance wherein stable ink discharging can be continuously conducted over a long period of time to continuously provide high quality prints even in the case where highly alkaline ink is used.

Claims: An ink jet head including a plurality of discharging outlets serving to discharge ink, a substrate for an ink jet head, said substrate including a plurality of energy generating elements capable of generating an energy for discharging ink from said plurality of discharging outlets and wirings electrically connected to said energy generating elements, and a plurality of ink pathways each having an ink flow path wall of forming one of the ink pathways by joining to said substrate, characterized in that each of the ink flow path walls is constituted by a specific epoxy resin composition (a) which is in the liquid state at room temperature, said epoxy resin composition (a) comprising, as a main component, a hardening epoxy resin (b) in the liquid state at room temperature having a molecular weight of 300 or more and having incorporated, an epoxy resin with a diepoxide structure having a siloxane bond (c) in an amount of 10 to 40 wt.-% versus the total amount of the hardening epoxy resin (b) and the siloxane bond possessing epoxy resin (c). An ink jet head according to claim 1, wherein the epoxy resin with a diepoxide structure having a siloxane bond (c) is of the following structural formula (I) or (II) (wherein, each of R 1 to R 4 is an alkyl group of 1 to 4 carbon atoms, an alkenyl group of 2 to 6 carbon atoms, a phenyl group, or a substituted aromatic group wherein R 1 to R 4 may be the same or different one from the other; each of R 5 and R 6 is an alkylene group of 1 to 8 carbon atoms, or a phenylene group wherein R 5 and R 6 may be the same or different one from the other; n is an integer of 1 to 1000.) An ink jet head according to claim 1, wherein the resin composition (a) is thermally curable. An ink jet head according to claim 3, wherein the resin composition (a) contains an amine series curing agent. An ink jet head according to claim 3, wherein the resin composition (a) contains a silane coupling agent. An ink jet head according to claim 5, wherein the silane coupling agent is in an amount of 1 to 10 parts by weight versus 100 parts by weight of the resin composition (a). An ink jet head according to claim 1, wherein the resin composition (a) is photo-curable. An ink jet head according to claim 7, wherein the resin composition (a) contains a compound capable of producing a cation upon the irradiation of light. An ink jet head according to claim 7, wherein the resin composition (a) contains a silane coupling agent. An ink jet head according to claim 9, wherein the silane coupling agent is in an amount of 1 to 10 parts by weight versus of 100 parts by weight of the resin composition (a). An ink jet head according to claim 1, wherein the hardening epoxy resin (b) has a viscosity of 10 to 100,000 cps. (mPas) An ink jet head according to claim 1, wherein each energy generating element comprises an electrothermal converting element capable of generating thermal energy. An ink jet head according to claim 1, wherein each energy generating element comprises a piezo electric element. An ink jet head according to claim 1, which is a full-line type ink jet head having a length corresponding to the entire width of the printing area of a printing medium on which printing is conducted. An ink jet head obtainable by forming a solid layer having an ink pathway-forming pattern on a substrate for an ink jet head, a plurality of energy generating elements capable of generating an energy for discharging ink from a plurality of discharging outlets and wirings electrically connected to said energy generating elements, applying a hardening ink flow path wall-forming material onto said substrate so as to cover the entire of said solid layer formed on said substrate, hardening said hardening ink flow path wall-forming material applied, and removing said solid layer to form a plurality of ink pathways, characterized in that said ink flow path wall-forming material comprises a specific epoxy resin composition (a) as specified in any one of the claims 1 to 14. An ink jet apparatus comprising: an ink jet head according to any one of the preceding claims and a means for transporting said printing medium on which printing is to be conducted by means of the ink jet head.

Inventors: IMAMURA ISAO, SHIBA SHOJI, SHIMOMURA AKIHIKO, IMAMURA, ISAO, SHIBA, SHOJI, SHIMOMURA, AKIHIKO, IMAMURA, ISAO, C/O CANON KABUHSIKI KAISHA, SHIBA, SHOJI, C/O CANON KABUHSIKI KAISHA, SHIMOMURA, AKIHIKO, C/O CANON KABUHSIKI KAISHA
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1994
Main classification: B41J2
IPC codes: B41J2, C08G59